Rudimentary child-order traits:
Oldest Child: Reliable, conscientious, aggressive, serious, intellectual, and stubborn. Natural leaders, perfectionists, achievers, people pleasers with a strong need for approval who don't like surprises. Need the attention and guidance they grew used to in their early years, but are less likely to say so. Over half of U.S. presidents are firstborns. In one word: Conscientious.
Only Child: The uber-oldest child. Even more responsible and a perfectionist. Tend to hang out with people older than themselves. In one word: Intellectual.
Middle Child: Independent, inventive, laid back, easy-going, and spontaneous. Read people well, see all sides of a situation, and act as peacemaker. Secretive with their thoughts and feelings, but also attention grabbers. Middle children build a very tight knit group of friends and peers outside the family. Middle children are the hardest to pin-down so the above characteristics may contradict each other. They seek approval of, but often are the complete opposite from the oldest sibling. In one word: Agreeable.
Youngest Child: Social, outgoing, secure, creative, financially irresponsible, just want to have a good time, love the limelight, charming, manipulative, spoiled, and helpless. In one word: Extravert.
from CBS news
These generalizations are, of course, muddled by age differences, sex, mixed families, new marriages etc... But you may find they apply to you or those you know. Generalizations like these can help us to accept our own characteristics or better understand why those around us act the way they do.
Check out your Romantic Compatibility according to your birth order HERE CLICK.
J and I are an First Born-Last Born mix, which is very compatible for pretty obvious reasons. I still have not gotten used to the idea of being married and every time I hear "your husband," I still giggle. Probably because I am a youngest child.